The present invention relates to electrical circuits which produce an output signal that has one of two signal levels determined in response to input signals from a pair of momentary contact, normally open switches; and more particularly, to such circuits for use in operating a cruise control system of a motor vehicle.
A motor vehicle often has a cruise control to maintain the speed of the vehicle at a relatively constant level set by the vehicle driver. The circuitry of a typical cruise control has an input to which a given voltage level must be applied continuously in order for the cruise control to remain activated. That input usually is connected to a switch that is stable in both the open and closed states, at which the cruise control is turned on and off respectively. A normally open switch also is provided for setting the vehicle speed to be maintained and for disabling the cruise control so that the vehicle can coast. Another normally open switch is alternately operated to resume cruise control operation from the vehicle coasting mode and to increase the set speed during normal operation to accelerate the vehicle.
In order to minimize a number of individual actuator elements that the vehicle driver must locate and operate, it is proposed to combine the normally open switches as part of a rocker switch mechanism. This allows the vehicle driver to push one side of the rocker mechanism to operate one normally open switch and to push on the other side of the rocker mechanism to operate the other normally open switch. When released by the vehicle driver, the rocker mechanism returns to a center position in which both of the normally open switches are in an open state.
It is preferable to provide a similar appearing and operating rocker switch to turn on and off the cruise control and thus use momentarily closing, normally open switches for that purpose. However, the on-off input to a conventional cruise control circuit requires a continuous voltage level to maintain the circuit in the activated state and momentarily closing, normally open switches do not provide that required continuous voltage level.
As a result, additional circuitry is necessary to interface such switches to the on/off input of the cruise control. Several types of well-known electrical circuits are able to toggle an output between one of two continuous signal levels in response momentary input signals. For example, flip-flops and latching circuits provide this function and are available in integrated circuit form.
It is also desirable that the switch signal interface circuit be relatively compact in order to fit within the steering wheel of the motor vehicle. Therefore, it is not convenient to produce the interface circuit from discrete electrical components. Further, commercially available latch and flip-flop integrated circuits have packages with 14 or 16 pins making them relatively large for this application. Similarly, standard NAND or NOR gate integrated circuits, which could be used to fabricate a flip-flop or latch, also have a minimum of 14 pins. Thus, although it is desirable to use a commercially available integrated circuit to convert the cruise control switch signals, the obvious circuit components are available only in relatively large packages.